Close-coupled process for improving the stability of soybean oil

Abstract

A close-coupled method of treating unrefined, unbleached soybean oil to produce a stable edible frying oil. The close-coupled process involves performing a series of steps to refine and bleach unrefined, unbleached soybean oil in a continuous sequence without intermediate storage and without substantial exposure to oxygen in the air which can lead to oxidation of heated oil, as follows: treating unrefined, unbleached soybean oil with a caustic agent; heating and water washing the treated soybean oil; degassing the soybean oil to remove a substantial portion of any oxygen and water entrained in the oil; dispersing into the oil a minor amount of finely divided, activated metallic salts and oxides including bleaching earths, clays, etc.; and heating the resulting dispersion in a carbon dioxide atmosphere. The treated oil is then degassed to remove entrained carbon dioxide, filtered to remove particulates and then cooled to provide a refined, bleached soybean oil.

We claim: 
     
       1. A close-coupled method for improving the odor and flavor stability of unrefined, unbleached soybean oil at a temperature of about 350 degrees F. to 400 degrees F., said method comprising performing a series of steps in continous sequence without intermediate storage and without substantial exposure to oxygen in the air, as follows: mixing unrefined, unbleached soybean oil with a caustic agent;   water washing the caustic-treated, unbleached soybean oil to produce refined, unbleached soybean oil;   degassing the wet refined soybean oil under vacuum to remove a substantial portion of oxygen and water entrained in said wet oil;   dispersing in said degassed oil a minor amount of a treating agent for bleaching said oil, said treating agent consisting essentially of finely divided, activated metallic salts or oxides;   heating the dispersion;   contacting the heated dispersion with carbon dioxide for a predetermined time to bleach and stabilize said heated oil;   degassing the treated oil to remove a substantial portion of the carbon dioxide from said treated oil;   filtering the degassed treated oil to remove the spent treating agents; and   cooling the filtered oil to produce refined, bleached soybean oil having improved odor and flavor stability at said temperature of about 350 degrees F. to 400 degrees F.   
     
     
       2. The close-coupled method according to claim 1 in which the unrefined, unbleached soybean oil is saturated with an inert gas immediately subsequent to the first degassing step. 
     
     
       3. The close-coupled method according to claim 1 in which the water washing step comprises the steps of: contacting said oil with hot wash water to form an emulsified oil mixture; and   centrifuging said emulsified oil mixture to separate a waxy aqueous phase from the oil.   
     
     
       4. The close-coupled method according to claim 1 in which the first degassing step is conducted under a vacuum of at least one-half atmosphere. 
     
     
       5. The close-coupled method according to claim 1 in which the first degassing step includes dehydrating said oil during degassing. 
     
     
       6. The close-coupled method according to claim 1 in which the treating agent further comprises a minor amount of activated carbon. 
     
     
       7. The close-coupled method according to claim 1 in which the step of heating the dispersion is carried out at a temperature of from about 212 degrees F. to about 260 degrees F. 
     
     
       8. The close-coupled method according to claim 1 in which the step of contacting with carbon dioxide is carried out for between about 10 minutes and about 6 hours. 
     
     
       9. The close-coupled method according to claim 1 in which the step of contacting with carbon dioxide further includes heating the dispersion to maintain the reaction temperature necessary to stabilize the oil. 
     
     
       10. The close-coupled method according to claim 1 in which the second degassing step is carried out under a vacuum of at least one-half atmosphere. 
     
     
       11. The close-coupled method according to claim 1 in which the filtering step is carried out at a temperature of about 220 degrees F. to about 240 degrees F. in a nitrogen inerted filter. 
     
     
       12. A refined, bleached, soybean oil having odor and flavor stability at a temperature from about 350 degrees F. to about 400 degrees F. produced according to the close-coupling method of claim 1. 
     
     
       13. A close-coupled method for improving the odor and flavor stability of unrefined, unbleached soybean oil at a temperature of about 350 degrees F. to about 400 degrees F., said method comprising performing a series of steps in continuous sequence without intermediate storage and without substantial exposure to oxygen in the air, as follows: adding a caustic agent to the unrefined, unbleached soybean oil;   turbulently mixing the caustic agent with the oil;   centrifuging said oil and caustic agent mixture to remove the resulting soapstock;   contacting said oil with wash water to form an emulsified oil mixture;   centrifuging said emulsified oil mixture to separate a waxy aqueous phase from the refined oil;   degassing the wet refined soybean oil under a vacuum;   dehydrating said wet refined soybean oil during degassing;   dispersing in said wet oil a minor amount of an activated treating agent for bleaching said oil;   heating the dispersion at a temperature of from 212 degrees F. to 260 degrees F.;   contacting the heated dispersion with heated carbon dioxide for a period between 10 minutes and 6 hours to protect the oil from absorbing oxygen and further heating the heated dispersion to maintain the reaction temperature until the bleaching treament of the oil is completed whereby the stability of the oil is improved;   degassing the treated oil under a vacuum to remove a substantial portion of the carbon dioxide from said treated oil;   filtering the degassed treated oil to remove the spent treating agents; and   cooling the filtered oil to produce refined, bleached soybean oil having improved odor and flavor stability at said temperature of about 350 degrees F. to about 400 degrees F.   
     
     
       14. A close-coupled method for improving the odor and flavor stability of unrefined, unbleached soybean oil at a temperature from about 350 degrees F. to about 400 degrees F., said method comprising performing a series of steps in continuous sequence without intermediate storage and without substantial exposure to oxygen in the air, as follows: adding a caustic agent to the unrefined unbleached soybean oil;   turbulently mixing the caustic agent and the oil;   centrifuging said oil to remove the resulting soapstock;   contacting said oil with wash water to form an emulsified oil mixture;   centrifuging said emulsified oil mixtuer to separate a waxy aqueous phase from the refined oil;   degassing the wet refined soybean oil under a vacuum of less than 5 cm of mercury;   dehydrating said wet refined soybean oil during degassing;   dispersing in said oil a minor amount of an activated treating agent for bleaching said oil, said treating agent consisting essentially of bleaching earths or clays and a minor amount of activated carbon;   heating the dispersion at a temperature of from 212 degrees F. to 260 degrees F., said heating conducted at least paritally by a heat exchanger;   contacting the heated dispersion with heated carbon dioxide for a period between about 10 minutes to about 6 hours to protect the heated oil from absorbing oxygen and further heating the heated dispersion to maintain the reaction temperature until the bleaching treatment of the oil is completed whereby the stability of the oil is improved;   degassing the treated oil under a vacuum of less than 5 cm of mercury to remove a substantial portion of the carbon dioxide from said treated oil;   filtering the degassed treated oil at a temperature of about 220 degrees F. to about 240 degrees F. in a nitrogen inerted filter to remove the spent treating agents; and   cooling the filtered oil to produce refined, bleached soybean oil having improved odor and flavor stability at said temperature of about 350 degrees F. to about 400 degrees F.   
     
     
       15. A close-coupled process according to claim 1 wherein the metallic salts or oxides comprise bleaching earths or clays. 
     
     
       16. A close-coupled process according to claim 1 wherein the treating agent includes a minor amount of activated carbon. 
     
     
       17. A close-coupled process according to claim 13 wherein the treating agent includes a minor amount of activated carbon.